As this sort of exhaust gas analysis system, there is one including a constant volume sampling apparatus (hereinafter also referred to as a CVS apparatus) that controls mixed gas produced by mixing diluent gas in exhaust gas discharged from an engine to have a constant flow rate, and samples the mixed gas into a sampling bag.
When analyzing exhaust gas from a hybrid vehicle (HEV or PHEV) using the CVS apparatus, if even at the time of stopping an engine, mixed gas continues to be sampled into the sampling bag in the same manner as at the time of operating the engine, only the diluent gas is sampled at the time of stopping the engine, and therefore the exhaust gas in the sampling bag is diluted. As a result, an S/N ratio at the time of analyzing the sampled exhaust gas decreases to reduce analysis accuracy.
Therefore, Patent Literature 1 describes a method for, in order to prevent sampled exhaust gas from being diluted when an engine is stopped, stopping sampling into a sampling bag when the engine is stopped.
However, since the method as described above stops the sampling into the sample bag when the engine is stopped, a sampling amount in the sampling bag decreases, and therefore there occurs a problem that on occasions such as when introducing sampled exhaust gas into, for example, various analyzers, the amount of the exhaust gas is insufficient.
Further, the sampling into the sampling bag is stopped when the engine is switched from an operation state to a stop state, and therefore the exhaust gas remains in a flow path and the like constituting a CVS apparatus, thus possibly causing a measurement error.
In addition, some test may prescribe the continuation of sampling into a sampling bag over a predetermined sampling time (e.g., 505 seconds) at, for example, a flow rate proportional to a main flow rate of a CVS apparatus, and for such a test, the above method cannot be employed.